[codex-tui] exit when terminal is dumb (#9293)

Using terminal with TERM=dumb specifically mean that TUIs and the like
don't work. Ensure that codex doesn't run in these environments and exit
with odd errors like crossterm's "Error: The cursor position could not
be read within a normal duration"

---------

Co-authored-by: Josh McKinney <joshka@openai.com>

codex-rs/cli/src/main.rs

@@ -28,6 +28,7 @@ use codex_tui::ExitReason;
 use codex_tui::update_action::UpdateAction;
 use codex_tui2 as tui2;
 use owo_colors::OwoColorize;
+use std::io::IsTerminal;
 use std::path::PathBuf;
 use supports_color::Stream;
 
@@ -45,6 +46,7 @@ use codex_core::features::Feature;
 use codex_core::features::FeatureOverrides;
 use codex_core::features::Features;
 use codex_core::features::is_known_feature_key;
+use codex_core::terminal::TerminalName;
 use codex_utils_absolute_path::AbsolutePathBuf;
 
 /// Codex CLI
@@ -735,6 +737,25 @@ async fn run_interactive_tui(
         // Normalize CRLF/CR to LF so CLI-provided text can't leak `\r` into TUI state.
         interactive.prompt = Some(prompt.replace("\r\n", "\n").replace('\r', "\n"));
     }
+
+    let terminal_info = codex_core::terminal::terminal_info();
+    if terminal_info.name == TerminalName::Dumb {
+        if !(std::io::stdin().is_terminal() && std::io::stderr().is_terminal()) {
+            return Ok(AppExitInfo::fatal(
+                "TERM is set to \"dumb\". Refusing to start the interactive TUI because no terminal is available for a confirmation prompt (stdin/stderr is not a TTY). Run in a supported terminal or unset TERM.",
+            ));
+        }
+
+        eprintln!(
+            "WARNING: TERM is set to \"dumb\". Codex's interactive TUI may not work in this terminal."
+        );
+        if !confirm("Continue anyway? [y/N]: ")? {
+            return Ok(AppExitInfo::fatal(
+                "Refusing to start the interactive TUI because TERM is set to \"dumb\". Run in a supported terminal or unset TERM.",
+            ));
+        }
+    }
+
     if is_tui2_enabled(&interactive).await? {
         let result = tui2::run_main(interactive.into(), codex_linux_sandbox_exe).await?;
         Ok(result.into())
@@ -743,6 +764,15 @@ async fn run_interactive_tui(
     }
 }
 
+fn confirm(prompt: &str) -> std::io::Result<bool> {
+    eprintln!("{prompt}");
+
+    let mut input = String::new();
+    std::io::stdin().read_line(&mut input)?;
+    let answer = input.trim();
+    Ok(answer.eq_ignore_ascii_case("y") || answer.eq_ignore_ascii_case("yes"))
+}
+
 /// Returns `Ok(true)` when the resolved configuration enables the `tui2` feature flag.
 ///
 /// This performs a lightweight config load (honoring the same precedence as the lower-level TUI

codex-rs/core/src/terminal.rs

@@ -47,6 +47,8 @@ pub enum TerminalName {
     Vte,
     /// Windows Terminal emulator.
     WindowsTerminal,
+    /// Dumb terminal (TERM=dumb).
+    Dumb,
     /// Unknown or missing terminal identification.
     Unknown,
 }
@@ -131,7 +133,12 @@ impl TerminalInfo {
 
     /// Creates terminal metadata from a `TERM` capability value.
     fn from_term(term: String, multiplexer: Option<Multiplexer>) -> Self {
-        Self::new(TerminalName::Unknown, None, None, Some(term), multiplexer)
+        let name = if term == "dumb" {
+            TerminalName::Dumb
+        } else {
+            TerminalName::Unknown
+        };
+        Self::new(name, None, None, Some(term), multiplexer)
     }
 
     /// Creates terminal metadata for unknown terminals.
@@ -166,6 +173,7 @@ impl TerminalInfo {
                 TerminalName::GnomeTerminal => "gnome-terminal".to_string(),
                 TerminalName::Vte => format_terminal_version("VTE", &self.version),
                 TerminalName::WindowsTerminal => "WindowsTerminal".to_string(),
+                TerminalName::Dumb => "dumb".to_string(),
                 TerminalName::Unknown => "unknown".to_string(),
             }
         };
@@ -435,6 +443,7 @@ fn terminal_name_from_term_program(value: &str) -> Option<TerminalName> {
         "gnometerminal" => Some(TerminalName::GnomeTerminal),
         "vte" => Some(TerminalName::Vte),
         "windowsterminal" => Some(TerminalName::WindowsTerminal),
+        "dumb" => Some(TerminalName::Dumb),
         _ => None,
     }
 }
@@ -1136,6 +1145,15 @@ mod tests {
             "term_fallback_user_agent"
         );
 
+        let env = FakeEnvironment::new().with_var("TERM", "dumb");
+        let terminal = detect_terminal_info_from_env(&env);
+        assert_eq!(
+            terminal,
+            terminal_info(TerminalName::Dumb, None, None, Some("dumb"), None),
+            "dumb_term_info"
+        );
+        assert_eq!(terminal.user_agent_token(), "dumb", "dumb_term_user_agent");
+
         let env = FakeEnvironment::new();
         let terminal = detect_terminal_info_from_env(&env);
         assert_eq!(

codex-rs/tui/src/app.rs

@@ -84,6 +84,17 @@ pub struct AppExitInfo {
     pub exit_reason: ExitReason,
 }
 
+impl AppExitInfo {
+    pub fn fatal(message: impl Into<String>) -> Self {
+        Self {
+            token_usage: TokenUsage::default(),
+            thread_id: None,
+            update_action: None,
+            exit_reason: ExitReason::Fatal(message.into()),
+        }
+    }
+}
+
 #[derive(Debug)]
 pub(crate) enum AppRunControl {
     Continue,